With various manufacturing processes, a work material, such as a continuously running web or sheet material, is added to or depleted from a product formation. For example, in a paper mill, the formed paper web is continuously added to a rolled product formation. The web may then be unwound from the rolled product formation in the process of making other products, such as consumable paper products. For various manufacturing and quality control reasons, it is often necessary to know how much of the product remains on the product formation, or has been depleted from the product formation, without stopping or otherwise adversely affecting the manufacturing line.
The above issue also applies to the dispensing of a wide variety of consumable products. Whether for private home use or public use, the dispensing of paper products such as towels and tissues has resulted in many different types of manual and automatic dispensing devices for controlling quantities dispensed, as well as for determining how much of the paper product has been dispensed. For example, U.S. Pat. No. 7,780,380 describes a dispenser of stacked paper products (e.g., folded and stacked napkins or paper towels) wherein a sensor unit is carried by an inner side wall of the dispenser housing and is used for detecting when refill of the dispenser is needed. The sensor unit uses an infrared sensor to detect when a stack of the paper product falls below a low paper point. A narrow beam of infrared light is sent from an emitter and is picked up by an adjacent detector. When the top of the paper stack lies above the infrared sensor, the detector does not pick up infrared light. However, when the top of the paper stack falls below the infrared sensor, light from the emitter is visible to the detector and an appropriate low paper warning is generated.
The U.S. '380 patent also describes an automatic rolled product dispenser that detects the presence of a user and automatically dispenses a measured sheet of paper product. A mechanical lever is arranged on a pivot at one end and rests on the roll at the other end. A micro-switch or variable resistor located near the pivot detects changes in the pivoted position of the lever as the roll diameter decreases and generates a corresponding signal to a sensor unit that generates an indication of the amount of paper product remaining in the dispenser.
Other types of detection mechanisms are also suggested in the U.S. '380 patent, including purely electrical systems, purely mechanical systems, electro-mechanical systems, capacitive systems, and ultrasonic systems. Capacitive proximity sensors produce an electrostatic field that can sense paper and other non-metallic objects as well as metallic objects. Ultrasonic proximity sensors use a transducer to send and receive high frequency sound signals. The reflected sound has a shorter path when the paper is in proximity to the sensor.
Thus, the industry is continuously seeking new and improved dispensing systems that can accurately determine usage of the product without prohibitively adding to the cost of the dispenser or adversely affecting the product dispensing operation. It would be a significant benefit if the usage determination system and method could function without requiring physical alteration or modification of the monitored product.